This invention relates to shudderless, tripode, plunging, constant-velocity, universal joints.
One type of such a constant-velocity, universal joint comprises a first rotary member having a rotary axis, three trunnions extending from the first member, a roller mounted directly or indirectly on a spherical surface on each trunnion, such surface being provided by the trunnion itself or by a member rotatably mounted on the trunnion, the roller including a cylindrical bore which engages the spherical surface so that each roller can rotate, tilt and slide relative to its supporting trunnion, the centers of the spherical surfaces on all the trunnions lying in a plane perpendicular to said rotary axis, a second rotary member having a rotary axis, three grooves formed in said second rotary member so as to extend parallel to the rotary axis of the second rotary member, each roller being engaged with one of the grooves, the engagement between each roller and its associated groove being such that the orientation of the roller with respect to the second member is determined solely by said engagement. In such a joint there is relative radial movement between the spherical surface of the trunnion and the roller.
One known form of shudderless, plunging, tripode joint is shown in cross section in FIG. 1. Referring to this figure there is a spider or inner member 10 of the joint which has three trunnions, one of which is shown at 11. The trunnion has a part-spherical surface 12 which receives an inner roller 13 having a cylindrical bore 14. The inner roller 13 can slide and tilt relative to the trunnion and moves radially relative to the center of the trunnion when the joint is articulated and rotating. An outer roller 15 is mounted on the inner roller 13 to rotate relative thereto, there being a needle roller bearing 16 between the rollers 13 and 15. The parts of the roller assembly are kept together by two rings 17 and 18. The outer race of the joint is indicated at 19 and has three grooves, each groove being formed by a pair of opposed tracks one of which is shown at 20. The cross-sectional shape of each track is formed by two circular arcs which give a xe2x80x9cGothic archxe2x80x9d form and angular contacts between the track and the roller. The centers 21 of the spherical surfaces of all of the trunnions lie in a plane perpendicular to the rotary axis 21a of the spider.
When torque is to be transmitted from the outer race 19 to the spider 10 in an anticlockwise direction in FIG. 1, there is a reaction force F0 which acts from the trunnion to the inner roller 13 and thence to the outer roller 15. The force F0 is generally perpendicular to the rotary axis of the roller 13, ignoring friction. There is two-point contact between the roller 15 and the right-hand track 20 and the reaction forces are shown at F1 and F2. The roller 15 is able to rotate about the intersection of these forces at 22 and without further constraint would be unstable. Because the roller 15 is free to tilt about the intersection 22, in order for the roller to be stable it will also engage the left-hand track so that there will be one or more reaction forces such as F3 or F4 on the circumference of the roller and/or a force F5 on the upper surface of the roller which limits its tilting movement. These additional forces on the left-hand side of the roller are intermittent and are due to the fact that, as the trunnion 11 moves up and down through the roller bore 14, the position of the roller 15 relative to the outer race 19 can, in general, only be defined by two points of contact (i.e. those of the forces F1 and F2) instantaneously when the trunnion is in a certain position with respect to the roller so that other forces are generally required to determine the orientation of the roller. These intermittent other forces F3, F4 and F5 increase the resistance of the roller to rolling along the tracks and hence the plunge resistance of the joint, i.e the passive resistance. They may also cause the joint to generate a cyclic net axial force when it rotates with the rotary axes of the spider and outer race misaligned, this can give rise to shudder vibration in a vehicle in which the joint forms part of the driveline.
A similar arrangement is shown in FIG. 2 except that in this case the trunnion 22 is cylindrical and an inner roller 23 provides the part-spherical outer surface 24 which engages a cylindrical bore 25 of the outer roller 26. The inner roller 23 is mounted on the trunnion by a needle roller bearing 27 and can not tilt or slide relative to the trunnion. The outer roller 26 can rotate, tilt or slide relative to the trunnion and to the part-spherical outer surface 24 which moves up and down within the bore 25. The forces on the roller 26 are similar to those described in relation to the joint shown in FIG. 1 and are shown by the same reference characters.
Because in each of the above examples the rollers 15 and 26 can tilt, slide and rotate relative to the trunnions and because the rollers are xe2x80x9cshapedxe2x80x9d to fit the grooves, the orientation of each roller with respect to its associated groove is determined solely by the engagement of the roller with the groove. There are other configurations of tripode joints in which the orientation of each roller relative to the outer race is determined by the engagement of the roller with the groove.
There is described in WO 97/25545 a further type of tripode shudderless joint and reference is made particularly to FIG. 17. In this joint, the tripode trunnions are cylindrical and mounted on each trunnion by needle roller bearings is an inner roller with a part-spherical outer surface. This engages an outer roller with an inner spherical-surface. The outer roller can tilt with respect to the inner roller but any sliding radial movement takes place between the trunnion and the inner roller. The outer spherical surface does not move radially with respect to the outer roller so that, unlike the joint of the current invention as will be described below, the force between the trunnion and the roller assembly acts at a fixed position relative to the roller assembly. Therefore there may be no tendency for the roller assembly to twist about an axis parallel to the axis of the second member.
In the prior joint the outer roller has a trapezoidal outer surface which engages a track surface of corresponding shape. It is suggested that contact may take place between three faces of the outer roller and the track but this would seem to require a very accurate fit between roller and track. This is acknowledged by the fact that the roller and track inclined surfaces are described as facing one another with xe2x80x9ca gapless contact or a very small gapxe2x80x9d. In practice the two trapezoids will generally only be in contact on one or two of their sides.
WO 97/25545 also describes how the rollers are only in contact with the track surface through which torque is being transmitted. This may be achieved by making the driving track (i.e. the track through which torque is transmitted) narrower than the other track. This results in asymmetric grooves and a requirement for different components to be used on the left and right hand sides of a vehicle.
An object of the present invention is to reduce the resistance of the rollers to rolling along the tracks and thus to reduce the plunge resistance whilst ensuring that the rollers are stable and that there is continuous three-point contact between the roller and the track, without requiring the profiles of the roller and the track to be matched with extreme accuracy.
Another object of the invention is to provide a shudderless, tripode joint in which the stability of each roller is determined solely by its engagement with the driving track and there are no intermittent contacts between the roller and the other track.
Another object of the invention is to reduce the NVH (noise, vibration, harshness) associated with clearance in the joint by damping the backlash movement of the roller when the torque is reversed.
Another object of the invention is to provide a joint in which the grooves to receive the rollers have a simple form making the second rotary member or outer race easy to manufacture.
Another object of the invention is to provide a joint in which the grooves are symmetrical.
Another object of the invention is to provide a joint in which all the contacts between the roller and the track are Hertzian (as hereinafter described);
According to one aspect of the invention we provide a plunging, constant-velocity universal joint comprising a first rotary member having a rotary axis, three trunnions extending from the first member, a roller mounted directly or indirectly on a spherical surface on each trunnion, such surface being provided by the trunnion itself or by a member rotatably mounted on the trunnion, the roller including a cylindrical bore which engages the spherical surface so that each roller can rotate, tilt and slide relative to its supporting trunnion, the centers of the spherical surfaces on all the trunnions lying in a plane perpendicular to said rotary axis, a second rotary member having a rotary axis, three grooves formed in said second rotary member so as to extend parallel to the rotary axis of the second rotary member, each groove comprising spaced-apart track surfaces which extend parallel to the rotary axis of the second member, each roller being engaged with a track surface in one of the grooves, the engagement between each roller and its associated track surface through which torque is being transmitted being at three points which hilly determine the roller""s orientation with respect to the second member and wherein, when the joint is transmitting torque, each roller is only in contact with the track surface through which the torque is being transmitted.
According to another aspect of the invention we provide a plunging, constant-velocity universal joint comprising a first rotary member having a rotary axis, three trunnions extending from the first member, a roller mounted directly or indirectly on a spherical surface on each trunnion, such surface being provided by the trunnion itself or by a member rotatably mounted on the trunnion, the roller including a cylindrical bore which engages the spherical surface so that each roller can rotate, tilt and slide relative to its supporting trunnion, the centers of the spherical surfaces on all the trunnions lying in a plane perpendicular to said rotary axis, a second rotary member having a rotary axis, three grooves formed in said second rotary member so as to extend parallel to the rotary axis of the second rotary member, each groove comprising spaced-apart track surfaces which extend parallel to the rotary axis of the second member, each roller being engaged with a track surface in one of the grooves, the engagement between each roller and its associated track surface through which torque is being transmitted being at three points which fully determine the roller""s orientation with respect to the second member, wherein the contact vectors of the reaction forces at said three points, when projected on to a common plane perpendicular to the rotary axis of the second member, form a triangle, wherein the contact vector of the force between the roller and the spherical surface, when projected onto said common plane, intersects the two sides of the triangle formed by the projected contact vectors of the reaction forces acting at a radially innermost and radially outermost of said points, the radial positions of said points being measured with respect to the rotary axis of the second member and wherein, when the joint is transmitting torque, each roller is only in contact with the track surface through which the torque is being transmitted.
Preferably the track surfaces in each groove are symmetrical with respect to a plane (the plane of symmetry) containing the rotary axis of the second member.
Preferably two of said contact vectors of the reaction forces when projected on to said common plane intersect on the plane of symmetry, said two contact vectors being one of the reaction forces acting at the radially innermost or radially outermost of said points and the contact vector of the reaction force acting at the radially intermediate point.
A first track surface on which the radially innermost point or the radially outermost point and the radially intermediate point is situated may be cylindrical. Said first track surfaces on each side of the groove may be parts of the same cylinder.
The radially innermost or radially outermost point which is not on the first track surface may be on a second track surface which is cylindrical. The first and second track surfaces may have a common tangent where they meet.
When the joint is transmitting torque the rotary axis of each roller may be tilted with respect to the plane of symmetry of its associated tracks. Thus when the direction of torque transfer through the joint reverses, each roller moves into contact with a track surface through which torque is then being transferred and tilts about an axis parallel to the rotary axis of the second member until its orientation is determined by said three-point contact. The tilt movement of each roller is preferably in a sense opposite to the direction of rotation of the first member after the direction of torque transfer has been reversed.
Each trunnion may have a part spherical surface engaged with a cylindrical bore of an inner rotary member on which the roller, is rotatably mounted. Alternatively each trunnion may have a cylindrical surface on which is rotatably mounted an inner rotary member having a spherical outer surface engaged with a cylindrical bore of the roller.